Reclaimed asphalt includes reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAS), asphalt reclaimed from plant waste, and asphalt recovered from roofing felt, among other sources.
Asphalt pavement is one of the most recycled materials in the world, finding uses in shoulders of paved surfaces and bridge abutments, as gravel substitutes on unpaved roads, and as a replacement for virgin aggregate and binder in asphalt pavements. Recycled asphalt pavement is typically limited, however, to use as sub-surface “black rock” or in limited amounts in asphalt base and surface layers. The usefulness of recycled material in the critical surface layers is limited because asphalt deteriorates with time; it loses flexibility, becomes oxidized and brittle, and tends to crack, particularly under stress or at low temperatures. The effects are due to aging of the organic component of the asphalt, i.e., the bitumen-containing binder, particularly upon exposure to weather. The aged binder is also highly viscous. Consequently, reclaimed asphalt pavement has different properties than virgin asphalt and is difficult to process. Untreated RAP can be used only sparingly; generally, an asphalt mixture comprising up to 30 wt. % of RAP can be used as sub-surface black rock. Moreover, because of the higher demands of the pavement surface, untreated RAP use there is generally limited to 15-25%.
Reclaimed asphalt can be blended with virgin asphalt, virgin binder, or both (see, e.g., U.S. Pat. No. 4,549,834). Rejuvenating agents have been developed to increase the amount of reclaimed asphalt that can be incorporated in both the base and surface layers. Rejuvenating agents restore a portion of the asphalt paving properties and binder bitumen physical properties, such as viscoelastic behavior, so that the reclaimed asphalt properties more closely resemble those of virgin asphalt. Improving the properties of recycled asphalt, and particularly the properties of bitumen binder in RAP, allows increased amounts of RAP to be used in asphalt mixtures without compromising the properties and lifetime of the final pavement.
Commonly used rejuvenating agents for RAP include low-viscosity products obtained by crude oil distillation or other hydrocarbon oil-based materials (see, e.g., U.S. Pat. No. 5,766,333 or 6,117,227).
Rejuvenating agents of plant origin have also been described. See, for example, U.S. Pat. No. 7,811,372 (rejuvenating agents comprising bitumen and palm oil); U.S. Pat. No. 7,008,670 (soybean oil, alkyl esters from soybean oil, and terpenes used for sealing or rejuvenating); U.S. Pat. Appl. Publ. No. 2010/0034586 (rejuvenating agent based on soybean, sunflower, rapeseed, or other plant-derived oils); and U.S. Pat. Appl. Publ. No. 2008/0041276 (plasticizers for recycled asphalt that may be vegetable oils or alkyl esters made from vegetable oils). U.S. Pat. No. 8,076,399 describes a binder composition comprising a resin of vegetable origin, a vegetable oil, and a polymer having anhydride, carboxylic acid, or epoxide functionality, but this binder is not specifically taught for rejuvenation. Although vegetable oils can provide desirable softening of aged binders, they tend to have average-to-poor miscibility with binders, which typically have substantial polycyclic aromatic character. Consequently, vegetable oils are prone to leaching, and they do not help binders retain native oils.
Aged binders, especially those that are severely aged, have viscoelastic properties that respond less than virgin bitumen to temperature changes, i.e., they have lower “temperature sensitivity.” A desirable rejuvenator will have the ability to alter or restore this property in an aged binder, in addition to or separate from softening the aged binder. Temperature sensitivity can be evaluated using dynamic shear rheometry (DSR) techniques described in more detail below. Thus, temperature sensitivity and softening are both important, but they are distinct restoration modes for transforming aged binders to rejuvenated ones having properties more reminiscent of virgin binders.
More recently introduced are rejuvenating agents derived from cashew nut shell oil, which contain mostly cardanol, a phenolic compound having a C15 unsaturated chain (see, e.g., PCT Internat. Publ. Nos. WO 2010/077141 and WO 2010/110651). Such products are available commercially from Ventraco Chemie, B.V., such as RheoFalt® HP-EM.
Various fractions isolated from crude tall oil (CTO) distillation have been used in asphalt compositions, although they are not specifically taught for rejuvenation. See, for instance, U.S. Pat. Appl. Publ. No. 2010/0170417 (CTO distillation fractions as cutting solvents use in asphalt compositions); U.S. Pat. No. 8,034,172 (distilled or oxidized tall oil components for use in asphalt compositions); and U.S. Pat. Nos. 4,479,827 and 4,373,960 (patching compositions comprising asphalt, tall oil, and possibly an organopolysiloxane).
Esters made from tall oil fatty acid (TOFA), tall oil rosin, tall oil pitch, or downstream products of CTO, such as Monomer acid (a unique product described, e.g., in U.S. Pat. No. 7,256,162), dimer acids, or the like, have not been previously suggested for use as rejuvenating agents for reclaimed asphalt.
Rosin esters have been taught sporadically for use in asphalt compositions. For example, they can be stabilizers for asphalt pre-mixes (U.S. Pat. No. 4,207,231), components of liquid emulsions (U.S. Pat. No. 4,492,781) or hot-mix asphalt formulations (U.S. Pat. No. 6,221,428), or asphalt binder components (U.S. Pat. No. 8,076,399).
Improved rejuvenating agents for reclaimed asphalt are needed. In particular, the industry needs additives for reclaimed asphalt that can improve low-temperature cracking resistance and fatigue cracking resistance while maintaining good rutting resistance. Better rejuvenating agents would reduce the cost of road construction by enabling greater use of RAP in new pavements and reducing reliance on virgin, non-renewable binder and aggregate materials. A preferred rejuvenating agent would reduce the binder viscosity to a level comparable to that of virgin binder and would also lower the glass-transition temperature of the binder to allow for softer, more easily processed asphalt mixtures. Ideally, the rejuvenating agent would derive from renewable resources, would have improved miscibility with aged binder to reduce its tendency to migrate from the binder, would have improved temperature sensitivity, and could restore the original performance grading to the binder.